Acquisitions and Divestitures - Narrative (Details) € in Thousands, $ in Thousands					9 Months Ended
	Apr. 09, 2018 EUR (€)	Apr. 09, 2018 USD ($)	Mar. 09, 2018 USD ($)	Jan. 31, 2018 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Apr. 09, 2018 USD ($)
Business Acquisition [Line Items]
Proceeds from sale of business					$ 430	$ 0
Pure Water Solutions [Member]
Business Acquisition [Line Items]
Consideration transferred, liabilities incurred				$ 4,699
Payments to acquire businesses, gross				3,706
Stock purchase price, net of cash received				993
Accrued earnout related to acquisitions				$ 461
Pacific Ozone [Member]
Business Acquisition [Line Items]
Consideration transferred, liabilities incurred			$ 8,557
Payments to acquire businesses, gross			6,557
Stock purchase price, net of cash received			$ 2,000
Earn out payment, period			3 years
Accrued earnout related to acquisitions			$ 934
Evoqua Water Technologies S.r.l. [Member]
Business Acquisition [Line Items]
Proceeds from sale of business	€ 350	$ 430
Evoqua Water Technologies S.r.l. [Member] | Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member]
Business Acquisition [Line Items]
Disposal group, including discontinued operation, accounts receivable, net	344						$ 484
Disposal group, including discounted operation, cost and earnings in excess of billings on uncompleted contracts	225						277
Disposal Group, including discontinued operation, prepaid and other assets, current	283						348
Disposal group, including discontinued operation, goodwill	118						145
Disposal group, including discontinued operation, other assets, noncurrent	180						222
Disposal group, including discontinued operation, accounts payable	33						40
Disposal group, including discontinued operation, product warranty, current	516						625
Disposal group, including discontinued operation, other liabilities	€ 147						$ 181